January 26, 1899] 



NA TURE 



309 



liquefaction was carried out in which six mercury gasholders 

 were filled with six separate fractions of argon, each taken after 

 each successive fifth of the total argon had evaporated. These 

 fractions were next purified from any nitrogen accidentally 

 present by sparking with oxygen over caustic potash. After the 

 removal of the oxygen the density was determined. 



Density of Argon. 

 For a preliminary determination of the density of the various 

 samples a bulb of about 33 c.c. capacity was employed. It is 

 much easier to ensure the purity of a small sample of gas than 

 of a large one ; and it will be seen that very concordant de- 

 terminations are obtainable with a small quantity. The limit of 

 error is {irobably not greater than one part in a thousand. The 

 results are expressed in terms of O = 16. 



Capacity of bulb. Temp. 



(1) 32762 19-05' 



(2) „ 1570 



(3) J. 1700 



(4) -. 14-55 



(5) ., '5-*>o 



(6) „ 16-15 



Weight. Density. 



5351 003786 19-65 



7120 0-05265 1995 



6622 0-05012 1995 



749-S 0-05460 I9'9i 



7404 0-05389 19-97 



760-2 005501 19-95 



The spectrum of No. 4, examined later, showed a trace of 

 nitrogen ; the density of No. 6 was confirmed by other two 

 determinations, each made after further sparking. 



No. I was the first portion boiled ofl', and therefore its density 

 is lower than that of the other fractions, probably owing to its 

 still containing some neon and helium. The rest of the samples 

 have a constant density, approximately 19-95. 



A larger quantity of No. 5 was then purified by long-con- 

 tinued sparking, and its density was determined in a bulb of 

 greater capacity. To show the influence of such purification, 

 results are given, obtained before it was complete. The gas 

 under such conditions showed a trace of the nitrogen spectrum. 

 The portion last weighed was spectroscopically pure. 

 Cap.-icityofbulb. Temp. Pressure. Weight. Density. 



163-19 15-47° 767-1 0-27235 I9'93S 

 ,, 16 97 7648 O-269S5 19-914 



13 34 7428 0-26591 I9'952 

 ,, 12-95 741 '3 0-26586 19-961 



After the first of these determinations the gas was 

 passed over a mixture of red-hot magnesium and lime, and 

 subsequently over red-hot copper oxide, in order to remove 

 hydrogen. But after determining the density, the gas was 

 examined spectroscopically, and was found to contain hydrt)gen. 

 The gas was therefore again sparked, when the density 19-952 

 was found. This specimen was also examined spectroscopically, 

 and was found to be absolutely free from all visible traces of 

 impurity. The last weighing refers to the same sample of gas, 

 and was made as a control experiment. 



These results conclusively prove that the density of argon, 

 purified from its companions, does not differ greatly from that 

 obtained by Lord Rayleigh, viz. 19 94, nor by one of us, viz. 

 19-941. The true density may, we think, be safely taken as 

 the mean of the last two determinations, viz. 19-957. 



This corresponds with the mean of the four tru.stworthy de- 

 terminations with the small bulb, viz. Nos. 2, 3, 5, and 6, which 

 is 19-955- 



Refvaciivity of Argon. 



The refractivity oi pure argon was next determined. The 

 measurements were made according to the plan suggested by 

 Lord Rayleigh (Roy. Soc. Proc, vol. lix. p. 201). The samples 

 investigated were Nos. i, 2, 5, and 6. The comparison was 

 made with air. 



(1) 09620 Contains neon and helium. 



(2) 0-9687 



(5) 09647 Mean, 0-9665. 



(6) 09660 



The refractivity of a previous sample of argon, obtained from 

 the middle of the 15 litres, during the second liquefaction, was 

 0-9679, a number differing only slightly from that given above. 



The refractivity of argon containing krypton, which had a 

 density 20-oi, was much higher than the number given above 

 for pure argon, for it reached i -030 as a mean of two determin- 

 atioas. Evidently then the body possessing the high refractivity 

 was not present in No. 6 in greater proportion than in No. 2, 



NO. 1526, VOL. 59I 



otherwise the refractivity of No. 6 would have shown an in- 

 crease over that of No. 2. 



The refractivity of pure argon differs somewhat from the value 

 for crude argon found by Lord Rayleigh, viz. 0-961 (Roy. Soc. 

 Proc, vol. lix. p. 205), and also from that previously found by 

 ourselves, 0-9596. The removal of neon, which appears to 

 have a very low refractivity, and of helium, of which the re- 

 fractivity is 0-1238, accounts for the increased refractivity of a 

 sample from which they are absent. The gases which we have 

 recently found in air and in crude argon will form the subject of 

 a future communication. .Suffice it to say that the amount of 

 neon and helium is much more considerable than that of the 

 others, and that their effect on crude argon is, therefore, much 

 more marked on its density and refractivity. 



The change in its physical constants, caused by the mixture of 

 more recently discovered gases which it has been shown to con- 

 tain, is therefore exceedingly small, and does not call for any 

 serious alteration in the original paper on " -Vrgon, a new Con- 

 stituent of the Atmosphere." 



The Density of Argon at the Boiling Point of O.xygen. 



In an addendum to the original paper on argon (Phil. Trans., 

 A, 1S95, p. 239), the expansion of argon by rise of temperature 

 to 250% as well as its contraction by fall of temperature to - 88°, 

 was determined. There is a considerable difference between 

 the temperature at which nitrous oxide boils and that at which 

 oxygen boils, and it was thought worth while to ascertain 

 whether argon behaves as a normal gas down to the boiling 

 point of oxygen. Olszewski (/or. cit., p. 257) gives the boiling 

 point of argon as - 187°, and that of oxygen as — 182-7 ; at the 

 latter temperature, therefore, argon would not be far removed 

 from its own condensing point. The interesting question, of 

 course, is the possible polymerisation of argon at such a low 

 temperature. 



No sign of any polymerisation has been observed, as is shown . 

 by the following data : — 



Tempera 

 "C. 



Hydrogen Thermometer. 

 Volume. 



R. 



99-7 1091-5 1-0026 2-9362 



0-0 803-2 I -0000 2-9421 



^ 182-7 269 6 0-9953 29715 



Argon Thermometer. 



lOQ-I 1414-9 1-0026 38095 



00 1040-0 I -0000 3-S022 



- 1S27 353-2 0-9953 38930 



No correction has been made for the unheated or uncooled 

 stem of the thermometer ; but it is obvious that although the 

 lowest temperament lies close to the boiling point of argon, the 

 ratio of the values of PV/T of hydrogen and argon at that 

 temperature, as well as the others, is practically constant. 



" On the Boiling Point of Liquid Hydrogen under Reduced 

 Pressure." By James Dewar, F. R.S. 



The June number of the Proceedings of the Chemical Society 

 contains a paper by the author on "The Boiling Point and 

 Density of Liquid Hydrogen." A resistance thermometer 

 made of fine platinum wire, called No. 7 Thermometer, was 

 used in the investigation. It had been carefully calibrated, and 

 gave the following resistances at different temperatures : — 



Resist.ince. 

 Temperature. Ohms. 



+ 991° C. 7337 



+ 7S3 6859 



■l-5i'4 6-?8S 



+ 25-7 5857 



+ 07 5'338 



-78-2 3-687 



-182-6 1-398 



-193-9 I -136 



-214-0 0690 



These numbers suggest that with the resistance reduced to 

 zero, the temperature registered by the thermometer ought to be 

 - 244' C. At the boiling point of hydrogen, therefore, if the 

 law correlating resistance and temperature can be pressed to its 

 limits, a lowering of the boiling point of hydrogen by 5 or 6' C. 

 would produce a condition of affairs where the platinum would 

 have no resistance, or become a perfect conductor. Now we 

 have every reason to believe that hydrogen, like other liquids. 



